1. Field of Invention
This invention relates to thermally-responsive record material. It more particularly relates to such record material in the form of sheets coated with color-forming systems comprising chromogenic material, and acidic color developer. This invention particularly concerns a thermally-responsive record material capable of forming an image resistant to fade or erasure. The invention teaches a record material having improved image density retention.
2. Description of Related Art
Thermally-responsive record material systems are well known in the art and are described in many patents, for example, U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318; and 4,470,057 which are incorporated herein by reference. In these systems, basic chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark.
Thermally-responsive record materials have characteristic thermal responses, desirably producing a detectable image of certain intensity upon thermal exposure which can be in a selective pattern or manner.
A drawback of thermally-responsive record materials limiting utilization in certain environments and applications has been the undesirable tendency of thermally-responsive record materials upon forming an image to not retain that image in its original integrity over time when the thermally-responsive record material is exposed to environments of high heat. As a result, a high degree of care and control in handling or storing imaged thermally-responsive record materials is required. This loss of image density or fade can be a serious problem whenever the integrity of records is diminished through improper record storage.
To impart ability to a thermally-responsive record material to resist image fading in high heat environments would be an advance in the art and of commercial significance.
It is an object of the present invention to disclose a thermally-responsive record material having improved image retention and resistance to fade or erasure. The record material of the invention is remarkably resistant to fade or erasure from common external challenges particularly high heat such as in a 60.degree. C. oven over a 24-hour time period.